France urges citizens to leave north Cameroon after kidnap

France on Wednesday urged its citizens to leave northern Cameroon after seven members of a French family were seized in a kidnapping officials suspect was carried out by Nigerian Islamist group Boko Haram.

The family -- a couple, their children aged five, eight, 10 and 12 and an uncle -- were snatched in northern Cameroon by six gunmen on three motorbikes on Tuesday and officials said they had been taken across the border into Nigeria.

With the latest abduction, France has overtaken the United States as the country with the most number of hostages held abroad, with 15 nationals in captivity against nine Americans.

President Francois Hollande condemned the seizure as an "odious" act, saying: "This is the first time that children have been taken hostage in this manner."

"We are doing everything with the help of authorities in Cameroon and Nigeria to find our compatriots," government spokeswoman Najat Vallaud-Belkacem quoted Hollande as telling a cabinet meeting.

The French foreign ministry in a notice urged citizens in the far north "to leave the area as quickly as possible" and advised against travel to areas bordering Nigeria until further notice.

French authorities have launched a preliminary investigation into the "kidnapping staged by a terrorist organisation," a judicial source said. Such cases are routinely opened when crimes are committed against French citizens abroad.

The ministry could not say how many French citizens are believed to be in the north but 6,200 in total are registered as living in Cameroon.

French Defence Minister Jean-Yves Le Drian pointed the finger at Boko Haram but said it was not clear whether the kidnapping was linked to France's intervention against Islamist rebels in Mali.

"We believe that the Boko Haram sect carried out this kidnapping, but we don't yet have a claim of responsibility," Le Drian told France 2 television.

"These are groups that claim the same fundamentalism, who use the same methods, whether it's in Mali, Somalia or Nigeria," he said.